The present invention relates generally to a sewing machine provided with a machine head capable of sewing a string-shaped sewing material, such as a tape or cord, onto a fabric or other sewing workpiece through lock switching. More particularly, the present invention relates to an improved sewing machine that can bring a desired machine head to a non-operating or resting state by placing a needle bar in a jump sewing state.
Heretofore, there have been known multi-head sewing machines equipped with a plurality of machine heads, each of which includes: a vertically-driven needle bar having a sewing needle fixed to the lower end thereof, a fabric holder member movable vertically (i.e., in an up-down direction) in synchronism with the up-and-down movement of the needle bar; a rotary member provided concentrically with the needle bar and rotatable about the axis of the needle bar; and a guide rotatable together with the rotary member for directing a string-shaped sewing material toward the point of the sewing needle (i.e., needle point). Each of such machine heads is capable of sewing a string-shaped sewing material onto the sewing workpiece by lock stitching while controlling the rotation of the rotary member in accordance with a moving direction of a sewing workpiece based on predetermined embroidery data and adjusting the orientation of the guide so that the string-shaped sewing material can be appropriately directed toward the point of the sewing needle. Among examples of such sewing machines equipped with machine heads capable of sewing string-shaped sewing materials is one disclosed in Japanese Patent Application Laid-open Publication No. HEI-8-299639.
In order to rest or stop operation of the machine head in the sewing machine disclosed in the HEI-8-299639 publication, it is necessary to not only cut off, via a jump mechanism, transmission of a rotational driving force from a main shaft of the machine to the needle bar to thereby set the needle bar in a “jump sewing state” where the needle bar is prevented from moving in an up-down direction in response to rotation of the main shaft, but also evacuate upward the fabric holder member. Namely, the machine's main shaft extends through the machine head, and the machine head includes a needle bar mechanism that sews a string-shaped sewing material onto a sewing workpiece by moving the needle bar of the machine head up and down through controlled rotation, by a machine motor, of the main shaft. The machine head further includes the jump mechanism that cuts off the driving force transmission from the main shaft to the needle bar. As well known in the art, the jump mechanism is of a motor-driven type controlled by electrical signals. Drive arm is fixed to the shaft of a jump controlling motor provided on the machine head, and the drive arm is caused to pivot, by the jump controlling motor responsive to a predetermined jump sewing signal (electrical signal), between a predetermined standby position and a predetermined jump-effecting position. The drive arm is normally urged, by a biasing means, to be located in the standby position. As the drive arm pivots to the jump-effecting position, a lifting/lowering drive member for vertically moving the needle bar up and down is rotated, so that the lifting/lowering drive member and the needle bar are operatively disconnected from each other and thus the needle bar is brought to the “jump sewing state” to stop its up-and-down movement. By the needle bar brought to the jump sewing state during the course of sewing, it is possible to form a long stitch, i.e. perform so-called “jump sewing”. Further, by continuously keeping the needle bar in the jump sewing state, the operation of the machine head itself can be stopped.
In addition to the jump controlling motor, the machine head is provided with a holder controlling motor for moving the fabric holder member up and down. During sewing operation of the sewing machine, the holder controlling motor vertically drives the fabric holder member in synchronism with the up-and-down movement of the needle bar, while, during rest or stoppage of the sewing machine, the holder controlling motor evacuates the fabric holder member far above a normal sewing stroke. While the fabric holder member is in the evacuating position and even when the holder controlling motor can not appropriately drive the fabric holder member for some reason, the fabric holder member lowers or descends in response to the downward movement of the needle bar by a component part, fixed to the needle bar, hitting a component part of a fabric holder drive mechanism as the needle bar driven by the main shaft descends, so as to avoid possible troubles, such as breakage of component parts.
In case there has occurred a sudden power failure during operation of the sewing machine, all of the motors driving the sewing machine stop operating or shut down. Of course, the machine motor, driving the main shaft, also stops operating; however, in the case of the motor stoppage due to a power failure or the like, the main shaft would continue to rotate for a while due to inertia, so that the needle bar moves up and down several times. Further, in some cases, the multi-head sewing machine is operated with just one or some of the plurality of machine heads, each capable of sewing a string-shaped sewing material, caused to operate with the remaining machine heads set in a resting state. In case there has occurred a sudden power failure during such operation of the multi-head sewing machine, not only the needle bar in each machine head set in the operating state but also the needle point in each machine head set in the resting state would move vertically up and down. Because, as noted above, desired stoppage of any of the machine heads is effected by the jump controlling motor driving the needle bar to shift to the jump sewing state and the jump controlling motor too stops operating due to the power failure, so that the drive arm is caused to pivot to the standby position, by means of the biasing means, to cancel the jump sewing state. Although the fabric holder member is evacuated upward in each machine head set in the resting state as noted above, the fabric holder member too descends if the needle bar descends, so that troubles, such as breakage of component parts, due to collision between the needle bar mechanism and the fabric holder mechanism.
However, if, in the multi-head sewing machine with only one or some of the plurality of machine heads operating with the remaining machine heads set in the resting state, the needle bars set in the non-operating state descend due to a power failure or the like during operation of the machine, there would occur a possibility of some component parts being deformed or broken. Namely, in the case where only one or some of the plurality of machine heads are in the operating state, a side of a rectangular-shaped embroidery frame, holding the sewing workpiece, may be located under any of the machine heads set in the resting state as the sewing machine operates. Thus, if the needle bars and fabric holder members of the machine heads set in the resting state descend due to a power failure or the like when a side of the embroidery frame is located under any of the machine heads set in the resting state, there would occur a significant inconvenience that the needle bar and fabric holder member collide against the side of the embroidery frame so that various component parts of the needle bar mechanism and fabric holder mechanism are deformed or broken.